I would agree with you on that. The 9R is for quick acceleration. 2.75 folds over and doesn't get the nose up like many of the stiffer tracks. Therefore, it's the opposite of what the 9R needs to "highlight" its capabilities.
Kesterke and Burandt don't run the 2.75. I can't speak for what Curtis runs because I've never seen his sled in person. Generally speaking, Professional's set ups aren't the best set ups for amateurs. The feedback here is most guys agree the 2.75 leaves more to be desired. Everyone is usually giving their opinion on what they have ridden, not what they saw someone running... I watched Caleb outclimb everyone with ease and do things all of us dream of on a 146 Boost with a 2.6 Composit track. I don't recommend that set up for anyone.